This macaroni and cheese, seasoned with spicy, umami-rich gochujang (a fermented Korean chili paste), uses the innovative mac and cheese formula from “Modernist Cuisine at Home.” Sodium citrate stabilizes the cheese instead of the typical flavor-deadening béchamel, so none of the cheddar’s sharp, salty, nutty, funky nuances are lost. Sodium citrate can be purchased online (don’t confuse it with citric acid). So the cheese melts easily, we find it best to shred it finely using the small holes on a box grater.